1. Field of the Invention
The invention relates to static inverters for converting electrical energy in the dc form to electrical energy in the ac form through static means. The present invention lies in the class of inverters in which the dc source produces a current through a single gain element connected in series with a primary winding of a power transformer and producing an ac output in the transformer secondary as the gain element is turned on or off. The invention represents a modification of known blocking oscillator configurations.
2. Description of the Prior Art
Static inverters of the class employing a dc source, a switching semiconductor device and a transformer are well known. The arrangements exist in either free running or the driven form. In either form, feedback windings may be used to control the semiconductor device. Recently, as represented by U.S. Pat. Nos. 3,914,680 and 4,002,999 to Hesler et al and assigned to the Assignee of the present invention, the transformer properties have been tailored to the requirements of the semiconductor in the inverter application, in particular to maximize the switching efficiency and to avoid full core saturation which unduly stresses the semiconductor devices. In both cited patents, the main core is provided with apertures, each of which divides the core into two localized branches. One branch is designed to saturate first, and upon saturation to reduce the regenerative and increase the degenerative feedback applied to the transistor so as to prevent full core saturation. The patented circuits have led to a reduction in the cost of such inverters, and a substantial improvement in the switching efficiency.
The present invention represents a further improvement on such arrangements in application to single transistor inverters in which energization is applied assymetrically to the transformer. In switching one device off without turning another one on, a new energy management problem is created. The high voltage surge may be very high, creating appreciable danger to the switching device, and at the same time a new mechanism is required for insuring that the transistor will come back on, after a period of non-conduction.